1. Field of the Invention
The present invention relates to chemical-mechanical polishing. More particularly, the present invention relates to a chemical-mechanical polishing pad.
2. Description of the Related Art
For very large scale integration (VLSI) or even ultra large scale integration (ULSI), chemical-mechanical polishing is the only technique that provides global planarization.
A general CMP apparatus is shown in FIGS. 1A through 1C. FIGS. 1A and 1B are respective side and top views showing a conventional chemical-mechanical polishing machine. Referring to FIG. 1A and FIG. 1B, a conventional chemical-mechanical polisher comprises a polishing table 10, a polishing pad 12 on the polishing table 10 and a polishing head 14 on the polishing table 10. During polishing, the polishing head 14 is used to hold the back of wafer 16. A duct 17 carries the slurry 18 to the polishing pad 12, and polishing is performed by spinning the polishing head 14 to remove uneven layers over the surface of the wafer 16.
FIG. 1C is schematic cross-sectional view showing the structure of polishing head 14 according to FIG. 1A. An air chamber 20 is at the top of the polishing head 14. The air chamber 20 exerts pressure on a wafer carrier 22 to bring the wafer 16 into close contact with the polishing pad 12. The wafer carrier 22 firmly holds the wafer 16 to enhance polishing performance. A wafer ring 24 underlies the wafer carrier 22 and surrounds the wafer 16, so that the wafer 16 is fixed in place by the wafer ring 24. Additionally, an insert pad (not shown) is provided between the wafer carrier 22 and the wafer 16.
FIG. 2 is schematic, top view showing the polishing pad 12 according to FIG. 1B. Referring to FIG. 2, the slurry 18 easily conglomerates in annular grooves around center as the duct 17 carries the slurry 18 to the polishing pad 12. This phenomenon makes it difficult for the slurry 18 to flow into the polishing head 14; therefore there is not enough slurry 18 in the polishing head 14. The uneven distribution of slurry 18 affects uniformity and degree of planarization of the wafer 16 while polishing is performed.